Switching network for circuit with multiple power sources

Abstract

A power supply circuit drives a load with first and second power sources. The power supply circuit has a switching network comprising a first switch and an interlock switch. A first circuit section connects the first power source to the load only when both the first switch and the interlock switch are on, and a second circuit section connects the second power source to the load only when both the first switch and the interlock switch are on. The switching network provides isolation between the first and second circuit sections.

What is claimed is: 
     
       1. A power supply circuit for driving a load with a first power source and with a second power source, comprising: (a) a switching network comprising a first switch and an interlock switch;   (b) a first circuit section for connecting the first power source to the load only when both the first switch and the interlock switch are on; and   (c) a second circuit section for connecting the second power source to the load only when both the first switch and the interlock switch are on, wherein the switching network provides isolation between the first and second circuit sections.   
     
     
       2. The circuit of claim 1, wherein the power supply circuit is incorporated in a power module that is seatable in a housing. 
     
     
       3. The circuit of claim 2, wherein the power module comprises a pressure-sensitive portion of the interlock switch mounted on the power module such that the pressure-sensitive portion is depressed, thereby turning on the interlock switch, when the power module is fully seated in the housing. 
     
     
       4. The circuit of claim 1, wherein the first power source is an AC power source and the second power source is a DC power source. 
     
     
       5. The circuit of claim 1, wherein the first switch is a single-pole double throw switch and the interlock switch is a double-pole double-throw switch. 
     
     
       6. The circuit of claim 1, wherein: the first circuit section comprises a first connection network having a first transistor in series with the load;   the first transistor is intercoupled with the first connection network so that, when the base terminal of the first transistor is not coupled to ground, the first transistor is on, thereby causing the first power source to be applied to the load;   the second circuit section comprises a second connection network having a second transistor in series with the load and a third transistor coupled to the base of the second transistor;   the second and third transistors are intercoupled with the connection network so that, when the base terminal of the third transistor is coupled to ground, the second transistor is on, thereby causing the second power source to be applied to the load;   the first switch and the interlock switch are configured and coupled to the first and second circuit sections so that the base terminal of the first transistor is not coupled to ground, and the base terminal of the third transistor is coupled to ground, only when both the first switch and the interlock switch are in an on position.   
     
     
       7. A power supply circuit for driving a load with a first power source and with a second power source, comprising: (a) a first circuit section for connecting the first power source to the load only when a first base terminal is not coupled to ground;   (b) a second circuit section for connecting the second power source to the load only when a second base terminal is coupled to ground; and   (c) a switching network comprising a single-pole double-throw first switch and a double-pole double-throw interlock switch having first and second interlock switches, wherein the first switch couples the first base terminal to ground in an off position and couples a switch node to ground in the on position; the first interlock switch couples the first base terminal to ground only in an off position; and the second interlock switch couples the switch node to the second base terminal only in an on position.   
     
     
       8. The circuit of claim 7, wherein: the first circuit section comprises a first connection network having a first transistor in series with the load, wherein the first base terminal is a base terminal of the first transistor and the first transistor is off only when the first base terminal is coupled to ground; and   the second circuit section comprises a second connection network having a second transistor in series with the load and a third transistor coupled to the base of the second transistor, wherein: the second base terminal is a base terminal of the third transistor, the third transistor is off only when the second base terminal is coupled to ground, and the second transistor is off only when the third transistor is on.